Structures comprising two or more magnetic layers that are coupled via an intervening coupling layer may be employed for magnetic memory devices, magnetic sensors (e.g. magnetoresistive sensors), and/or other applications. Typically, the magnetic moments (or magnetic directions or magnetization directions) of such magnetic layers are coupled at 0° relative to one another (which may be referred to as being ferromagnetically coupled) or are coupled at 180° relative to one another (which may be referred to as being antiferromagnetically coupled and/or as antiparallel coupling). While ferromagnetically coupled magnetic layers and antiferromagnetically coupled layers have proven to be useful, there are a number of drawbacks associated with having the magnetic layers coupled at 0° relative to one another. For example, for magnetoresistive sensor applications, such as those employing tunnel-magnetoresistance (TMR) or giant-magnetoresistance (GMR), such drawbacks include, without limitation: ambiguities in the resistive response to the directionality of the applied field and non-linearity of the resistive response to the applied field. As another example, for memory device applications, switching between stable states is typically reliant on probabilistic thermal variation, leading to drawbacks that include, without limitation: undesirably long switching times, undesirably high error rates and undesirably high switching current or switching power.
U.S. Pat. No. 7,199,984 discloses a PtMn coupling layer having an atomic concentration of 25-75% Pt and 25-75% Mn for coupling CoFe or NiFe magnetic layers with orthogonally oriented magnetization directions. Such orthogonally oriented magnetization directions represent an example of non-collinearly coupled (NCC) magnetic layers.
The PtMn coupling layer disclosed by U.S. Pat. No. 7,199,984 has a thickness of less than 10 nm and is preferably between 1.5 and 5.0 nm. PtMn coupling layers of the type disclosed by U.S. Pat. No. 7,199,984 have weak coupling strength and low saturation fields. Because of this weak coupling strength, sensors which employ coupling layers constructed according to the teachings of U.S. Pat. No. 7,199,984 may only be employed for sensing external magnetic fields less than approximately 1000 Oe. There is a desire for magnetic sensors with the ability to sense stronger external magnetic fields. In addition, PtMn coupling layers of the type disclosed by U.S. Pat. No. 7,199,984 have been determined to require thicknesses of greater than about 1.2 nm. Below this thickness, diffusion of material from the adjacent magnetic layers destroys the orthogonal non-collinear coupling. There is a general desire to make magnetic structures (e.g. non-collinearly coupled magnetic structures) that are as small as is reasonably possible.
Still further, the coupling layers disclosed by U.S. Pat. No. 7,199,984 tend to revert to coupling at 0° after annealing (e.g. at temperatures greater than 200° C. or even at lower temperatures). For example, the inventors created a structure according to the teachings of U.S. Pat. No. 7,199,984 where a Mn coupling layer having a thickness of 1.4 nm was interposed between Co magnetic layers. FIG. 1 shows the normalized magnetization of this structure as a function of external magnetic field H without annealing (dark circles) and with annealing at 200° C. (open circles). As can be seen from FIG. 1, the magnetic structure having a coupling layer of Mn that is annealed at 200° C. does not exhibit non-collinear magnetic coupling between the Co magnetic layers of the magnetic structure (e.g. the annealed magnetic structure is fully saturated even with a very small applied magnetic field (e.g. 100 Oe)). Many applications for coupled magnetic layers, such as applications which make use of the tunnel magnetoresistance (TMR) effect, require annealing (e.g. at temperatures greater than 200° C.) to increase sensitivity and increase the magnitude of resistance changes across a magnetoresistive layer. Annealing may also be required to align antiferromagnetic layers in particular applications. There is a general desire for magnetic structures comprising two or more magnetic layers that are coupled via an intervening coupling layer where the magnetic structure, or a portion thereof may be annealed (for example, at temperatures above 200° C.) without undesirably affecting the coupling (e.g. non-collinear coupling) of the two or more magnetic structures. Structures fabricated according to the techniques described in U.S. Pat. No. 7,199,984 exhibit non-collinear coupling at 90° only. There is a general desire to provide structures that exhibit non-collinear coupling at angles other than 90°.
U.S. Pat. No. 6,893,741 discloses a RuFe coupling layer having an atomic concentration of less than or equal to 60% Fe and at least 40% Ru for antiferromagnetically coupling specific Co alloy (such as CoPtCrB) magnetic layers (i.e. with magnetization directions at an angle of 180° with respect to one another). U.S. Pat. No. 6,893,741 discloses an exchange field (also commonly referred to as a saturation field) of 2750 Oe for Ru65Fe35 as compared to 1575 Oe for a pure Ru coupling layer. To the extent that the assertions in U.S. Pat. No. 6,893,741 are accurate, such structures could only be employed for sensing external magnetic fields under less than approximately 1375 Oe. There is a desire for magnetic sensors with the ability to sense stronger external magnetic fields, whether such sensors comprise antiferromagnetically coupled magnetic layers and/or non-collinearly coupled magnetic layers. Similarly, the coupling layers disclosed by U.S. Pat. No. 6,893,741 could not be employed for the purpose of pinning a magnetic layer in applications where external fields of greater than 2750 Oe may be experienced. Further, the coupling layers disclosed by U.S. Pat. No. 6,893,741 do not allow coupling at angles other than 180° and, consequently, suffer from the above-described drawbacks of antiferromagnetic coupling.
There is a general desire for magnetic devices comprising coupling layers for coupling magnetic layers at non-collinear angles (i.e. angles greater than 0° and less than 180°). It may be desirable for such magnetic devices to have high coupling strength and/or high saturation fields. There is a general desire for magnetic devices comprising coupling layers for coupling magnetic layers at non-collinear angles other than 90° (i.e. angles other than 0°, 90° and 180°). There is a general desire for magnetic devices comprising coupling layers for coupling magnetic layers at non-collinear angles (i.e. angles other than 0° and 180°) after annealing. There is a general desire for magnetic devices comprising coupling layers that are practical to manufacture without requiring overly stringent tolerances on atomic composition and atomic distribution and coupling layer thickness.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.